Packet data latency is one of the performance metrics that vendors, operators and end-users (e.g., via speed test applications) regularly measure. Latency measurements are performed in all phases of the lifetime of a radio access network system such as when verifying a new software release or system component, when deploying a system and when the system is in commercial operation.
One performance metric that guided the design of Long Term Evolution (LTE) was to provide shorter latencies than previous generations of 3GPP radio access technologies (RATs). By doing so, LTE is recognized by end users as providing faster access to the Internet and shorter data latencies than these previous generations. Packet data latency is important not only for the perceived responsiveness of the system but also indirectly influences the throughput of the system. HTTP/TCP is the dominating application and transport layer protocol used on the Internet. According to HTTP Archive (http://httparchive.org/trends.php), the typical size of HTTP based transactions over the Internet range from tens of kilobytes to one megabyte. In this range, the TCP slow start period is a significant part of the total transport period of the packet stream. During TCP slow start, the performance is limited by latency. Hence, the average throughput can be improved by reducing the latency for this type of TCP based data transactions.
Furthermore, radio resource efficiency can be improved by reducing latency. For instance, lower packet data latency could increase the number of transmissions that are possible within a certain delay bound. Hence, higher Block Error Rate (BLER) targets could be used for data transmissions, resulting in freeing up radio resources to improve the capacity of the system.
Another area to reduce packet latency is to reduce the transport time of data and the associated control signaling. For instance, in LTE Release 8, a transmission time interval (TTI) corresponds to one subframe of length (i.e., 1 millisecond) that is composed of two slots of 0.5 milliseconds each. One such TTI is constructed using fourteen orthogonal frequency division multiplexing (OFDM) or single-carrier, frequency-division multiple access (SC-FDMA) symbols in the case of normal cyclic prefix (CP) and twelve OFDM or SC-FDMA symbols in the case of extended CP. For LTE Release 13, shorter TTIs (i.e., shorter than the LTE release 8 TTI) are being investigated. These shorter TTIs may be any duration in time and may include resources on a number of OFDM or SC-FDMA symbols that are within the LTE Release 8 TTI (i.e., 1 millisecond). Short TTI is a term used thereafter to refer to a transmission of shorter duration than LTE Release 8 transmission duration of 1 ms. For instance, the duration of a short TTI may be 0.5 milliseconds (i.e., 7 OFDM or SC-FDMA symbols for normal CP), which corresponds to a slot based transmission. Another example is a short TTI of 2 symbols, which corresponds to a subslot based transmission.
With short TTIs, there is a need for improved techniques to perform power control of physical channels in a communication system such as for transmission on physical channels having short TTIs. In addition, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and embodiments, taken in conjunction with the accompanying figures and the foregoing technical field and background.
The Background section of this document is provided to place embodiments of the present disclosure in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.